McIlroy opened Thursday with an up-and-down round of even-par 72, four birdies and four bogeys, and trails early leaders Padraig Harrington (68) and Billy Horschel by four shots.

McIlroy, who started on No. 10, played with Match Play champion Matt Kuchar (72) and 19-year-old rookie Jordan Spieth (71).

Spieth had a share of the lead at 4 under before a triple-bogey 8 on the par-5 eighth hole.

McIlroy was 2 under early in his round, which began on No. 10 on the difficult 7,435-yard layout.

However, McIlroy found the water on the par-5 18th when his approach came up short — beginning a stretch of three straight bogeys. He was 1 under entering his final hole of the round, No. 9, and missed a 7-foot par putt to fall back to even.

The up-and-down round was hardly what McIlroy, who has just one top-10 finish this year, envisioned when he added the tournament to his schedule.

"More mental than anything else," McIlroy said. "It's just about limiting those mistakes. It's definitely more mental mistakes than physical."